This summary reviews publicly available information about the adverse impacts of land-based wind power on wildlife in North America and the status of our knowledge regarding how to avoid or minimize these impacts.

BACKGROUND: DOE NREL AND IBERDROLA RENEWABLES • INSET, L-R: EASTERN MEADOWLARK, PHOTO BY MATTHEW PAULSON, FLICKR • AMERICAN BALD EAGLE, PHOTO BY USFWS, FLICKR • HOARY BAT, PHOTO BY J. N. STUART, FLICKR

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Wind Turbine Interactions with Wildlife and Their Habitats

A Summary of Research Results and Priority Questions 

Last Updated with Latest Publicly Available Information: May 2018

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Wind Turbine Interactions with Wildlife and Their Habitats: A Summary of Research Results and Priority Questions

INTRODUCTION

W ind energy’s ability to generate electricity without carbon emissions is expected to reduce the risk of potentially catastrophic effects to wildlife from unmitigated climate

change. Wind energy also provides several other environmental benefits including substantially reduced water withdrawals and consumption and decreased emissions of mercury and other sources of air and water pollution associated with the burning of fossil fuels (NRC 2010).

The siting and operation of wind energy facilities also risk adverse impacts to wildlife, particularly to individual birds and bats (Arnett et al. 2008; Strickland et al. 2011). The potential for biologically significant impacts to wildlife continues to be a source of concern as populations of many species overlapping with proposed wind energy development are experiencing long-term declines due to habitat loss and fragmentation, disease, non-native invasive species, and increased mortality from numerous other anthropogenic activities (NABCI 2009; O’Shea et al. 2016).

To maximize wind energy's benefits while addressing the risk to wildlife, a first step is to better understand the extent of the risk and impact of wind energy development to wildlife. This summary reviews publicly available information about the adverse impacts of

SMOKY HILLS WIND FARM, PHOTO BY DRENALINE, WIKIPEDIA

BLUE-WINGED TEAL, PHOTO BY ANDREA WESTMORELAND, FLICKR

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Wind Turbine Interactions with Wildlife and Their Habitats: A Summary of Research Results and Priority Questions

land-based wind power on wildlife in North America and the status of our knowledge regarding how to avoid and minimize these impacts.

The amount of publicly-available, peer-reviewed research con-tinues to grow, reflecting the ongoing interest in understanding wind-wildlife interactions. To maintain the highest level of scientific rigor for this summary, we have emphasized research that has been published in peer-reviewed journals as well as publicly avail-able reports that have undergone expert, technical review.

This summary is updated and undergoes expert review on an an-nual basis. Literature citations supporting the information present-ed are denoted in parentheses; full citations can be found online at http://awwi.org/resources/summary-of-wind-wildlife- interactions/.

Organization of This SummaryConcerns about adverse impacts can be grouped broadly as direct or indirect impacts. We define direct impacts to include fatalities resulting from collisions with turbine blades or towers. Indirect impacts result from the effects of the construction and operation of a wind energy facility on a species’ use of habitat. These impacts may include displacement of a species from suitable habitat or de-mographic effects due to fragmentation of habitat or disturbance from the construction and operation of a wind facility. This sum-mary organizes statements about what is known and what remains uncertain regarding the adverse impacts of wind energy on wildlife in the following categories:

• Direct mortality

• Population level consequences of collision fatalities

• Avoidance and minimization of collision fatalities

• Habitat-based impacts on birds

Within each section, statements are ordered in decreasing level of certainty. The level of certainty reflects the “weight of the evidence” from multiple published studies on a subject of inter-est. A single study, although informative, is usually insufficient for drawing broad conclusions. Although more information is available on direct impacts to individual birds and bats, substantial uncer-tainty remains regarding potential population-level consequences of collision mortality and our ability to predict collision risk.

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INTRODUCTION (CONTINUED)

Installed wind energy capacity in the United States continues to grow and was estimated at nearly 89,000

megawatts (MW) at the end of 2017. The power ratings of turbines installed at new projects typically range from 1.5-3 MW, and turbine towers typically range in height from 80-100 m (260-330 feet). Tur-bine blades range in length from 38-50 m (200-260 feet) resulting in a maximum potential height of approximately 140 m (460 feet) and a rotor swept area of 0.45-1.34 hectares (1.1-3.3 acres). Blade tip speeds range from 220-290 km/hr (140-180 mph) under normal operating conditions. The perimeter of a wind facil-ity may encompass thousands of acres. The most current wind market informa-tion can be found at the American Wind Energy Association’s website.

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Wind Turbine Interactions with Wildlife and Their Habitats: A Summary of Research Results and Priority Questions

DIRECT MORTALITY

At many wind facilities, regular searches are con-ducted for birds and bats that may have collided with turbines. The number of studies reporting

results of collision fatality monitoring at operating land-based wind energy facilities has increased substantially over the years, and studies conducted at more than 100 projects are publicly available (Arnett and Baerwald 2013; Loss et al. 2013a; Erickson et al. 2014; Thompson et al. 2017). Proto-cols for carcass searches have become more standardized, facilitating comparisons of results from separate studies. Much uncertainty remains as to the distribution, timing, and magnitude of collision fatalities of both birds and bats. Some of this uncertainty reflects the lack of data from particular regions of the country, such as the southwestern U.S., where only a few publicly available fatality reports are available.

This section outlines what is known and where there is remaining uncertainty about the patterns of bird and bat collision fatalities, particularly in the continental U.S. We first examine patterns that apply to both birds and bats and then describe patterns specific to birds and specific to bats.

Birds and Bats

Fatalities of birds and bats have been recorded at all wind energy facilities for which results are publicly available.

We assume that most bird and bat collisions are with the ro-tating turbine blades, although collisions with turbine tow-ers are also possible. Fatality estimates of individual studies vary in how raw counts are adjusted for known sources of detection error and sampling intensity (Huso et al. 2016). Our understanding of these sources of error is improving, but comparisons or aggregations of fatality estimates, espe-cially if they include older studies (2006 or earlier), should be interpreted cautiously.

For birds, adjusted fatality rates from most studies range from three to six birds per MW per year1 for all species combined, and no publicly available study has reported more than 15 bird fatalities per MW per year (Strickland et al. 2011; Loss et al. 2013a; Erickson et al. 2014). There is relatively little variation in bird fatalities across regions for all species combined, although fatalities at sites in the Great Plains appear to be lower than sites in the rest of the U.S., and fatalities in the Pacific region may be significantly higher (Loss et al. 2013a). It is unknown to what extent these dif-ferences reflect the sample bias discussed earlier.

Adjusted bat fatality rates may be substantially higher than bird fatality rates, especially at facilities in the upper Mid-

1 Fatality rates are typically reported on a per turbine basis or per name-plate capacity (MW). We report fatality rates per nameplate capacity to account for differences in turbine capacity, which range from 100 kw to 3.0 MW or more, but we acknowledge that this reporting format also has difficulties.BLACK THROATED BLUE WARBLER, PHOTO BY KELLY COLGAN AZAR, FLICKR

LITTLE BROWN BATS, PHOTO BY USFWS, FLICKR

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Wind Turbine Interactions with Wildlife and Their Habitats: A Summary of Research Results and Priority Questions

west and eastern forests: two facilities within the Appala-chian region reported fatality levels of greater than 30 bats per MW per year, but there are also reports as low as one to two bats per MW per year at other facilities in the eastern U.S. (Hein et al. 2013). Recent analysis suggests that bat fatalities are inversely related to the percent of grassland cover in proximity to wind facilities (Thompson et al. 2017). On average, reported bat fatality rates are substantially lower at facilities in the western U.S. (Arnett and Baerwald 2013; Hein et al. 2013).

The lighting currently recommended by the Federal Aviation Administration (FAA) for installation on commercial wind turbines does not increase collision risk to bats and migrating songbirds. 

The FAA regulates the lighting required on structures taller than 199 feet in height above ground level to ensure air traffic safety. The number of bat and songbird fatalities at turbines using FAA-approved lighting is not greater than that recorded at unlit turbines (Kerlinger et al. 2010; Bennett and Hale 2014). One study (Bennett and Hale 2014) recorded higher red bat fatalities at unlit turbines compared to those using red aviation lights; no differences were observed for other bat species between lit and unlit turbines. For wind turbines, the FAA currently recommends strobe or strobe-like lights that produce momentary flashes interspersed with dark periods up to three seconds in duration, and they allow commercial wind facilities to light a proportion of the turbines in a facility (e.g., one in five), firing all lights synchronously (FAA 2007). Red strobe or strobe-like lights are frequently used.

The effect of turbine height and rotor swept area on bird and bat collision fatalities remains uncertain.

Some studies have suggested that bird and bat fatalities increase with tower height (Barclay et al. 2007; Baerwald

and Barclay 2009; Loss et al. 2013). However, tower height was found not to affect levels of bat fatali-ties at Canadian facilities (Zimmerling and Francis 2016), and studies on birds suggest that the relation-ship between tower height and bird collisions is more nuanced (Smallwood and Karas 2009). Taller turbines often have much larger rotor-swept areas, and it has been hypothesized that collision fatalities will increase due to the greater overlap with flight heights of nocturnal-migrating songbirds and bats (Johnson et al. 2002; Barclay et al. 2007). The vast majority (>80%) of avian nocturnal migrants typically fly above the height of the most common rotor-swept zone (<500 feet; <150 m) (Mabee and Cooper 2004; Mabee et al. 2006), and there is no evidence to date that nocturnal migrants form a disproportionately high number of collision fatalities during migration (Welcker et al. 2017).

It is unknown whether collision risk at standalone turbines is comparable to risk at individual turbines within large wind energy facilities.

Construction of single utility-scale turbines (1.5-2 MW) is growing rapidly in some regions of the country, especial-ly where opportunities for large utility-scale projects are limited or municipalities often supply their own electricity (e.g., Massachusetts). Fatality monitoring at single-turbine facilities is often not required, and published reports have not been available.

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GRASSHOPPER SPARROW, PHOTO BY SHEILA GREGOIRE, FLICKR

DIRECT MORTALITY (CONTINUED)

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Wind Turbine Interactions with Wildlife and Their Habitats: A Summary of Research Results and Priority Questions

Birds

A substantial majority of bird fatalities at wind energy facilities are small passerines.

Approximately 250 species of birds have been reported as collision fatalities at wind energy facilities for which data are available (Loss et al. 2013; Erickson et al. 2014). Raw counts of small passerines (<31 cm in length) account for approxi-mately 60% of fatalities reported in publicly available studies at U.S. wind facilities (Erickson et al. 2014). Small passerines comprise more than 90% of all landbirds (Partners in Flight Science Committee 2013). Searcher efficiency trials2 indicate that small birds have significantly lower detection rates than large birds (Peters et al. 2014), and the true proportion of passerine fatalities of all collision fatalities is uncertain. Most small passerine species are migratory, resulting in spring and fall peaks of bird fatality rates at most wind facilities (Strick-land et al. 2011; Erickson et al. 2014).

Diurnal raptors are relatively frequent fatalities, particularly in the western U.S. where these species are more common. Because these groups are far less abundant than passerines,

2 Searcher efficiency trials involve placement of bird and bat carcasses to estimate the number of carcasses missed by field technicians during fatality surveys. This estimate is combined with other sources of detection error, such as scavenger removal of carcasses, to adjust the “raw counts” of car-casses found during fatality surveys and provide a more accurate estimate of collision fatalities.

there is concern that the potential relatively high fatality rates are reflective of a higher vulnerability to collision. These higher raptor fatality counts may be partially due to higher detectability of large birds as described above (Peters et al. 2014).

The vulnerability to collision of native game birds (e.g., sage grouse and prairie chickens) is unknown, although pheas-ants have constituted a large proportion of reported fatali-ties at wind energy projects in the western U.S. (Strickland et al. 2011).

Fatalities of waterbirds and waterfowl, and other species characteristic of freshwater, shorelines, open water, and coastal areas (e.g., ducks, gulls and terns, shorebirds, loons

GOLDEN-CROWNED KINGLET, PHOTO BY ZANATEH, FLICKR

GOLDEN EAGLE, PHOTO BY ELSIE.HUI, FLICKR

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Wind Turbine Interactions with Wildlife and Their Habitats: A Summary of Research Results and Priority Questions

and grebes) are reported infrequently at land-based wind facilities (Kingsley and Whittam 2007; Gue et al. 2013), although this could change as more wind energy devel-opment occurs offshore or in regions where waterfowl abundance is high (Graff et al. 2016). The infrequent rate of fatalities of coastal birds at U.S facilities is somewhat different than that reported at coastal facilities in the Neth-erlands (Winkelman 1992; Stienen et al. 2008; Everaert 2014), but this could be due to the limited information from coastal wind facilities, particularly in the U.S. (Kings-ley and Whittam 2007; NAS 2007).

Repowering with newer, larger (≥ 1 MW) turbines may reduce raptor collision rates at wind facilities compared to older, smaller (40 - 330kW) turbines. 

The number of raptor fatalities on a per MW basis appear to be declining substantially (67 – 96% depending on the species) at the Altamont Pass Wind Resource Area as a re-sult of repowering: smaller, low-capacity turbines are being replaced with taller, higher-capacity turbines (Smallwood and Karas 2009; ICF International 2016). Larger turbines complete fewer rotations per minute, which may be partly responsible for reduced raptor collision rates (NAS 2007). In addition, older turbines that use lattice support towers offer more perching sites for raptors, encouraging higher raptor occupancy in the immediate vicinity of the rotor swept area (NAS 2007) than large, modern turbines on tubular support towers.

Bats

Migratory tree-roosting bat species are vulnerable to colliding with wind turbines. 

At least 24 species of bats have been recorded as collision fatalities in North America, but a large majority of fatalities reported to date are from three migratory tree-roosting species (the hoary bat, the eastern red bat, and the sil-ver-haired bat) which collectively constitute ~70% of the reported fatalities at wind facilities for all North American regions combined (Kunz et al. 2007; Arnett et al. 2008; Arnett and Baerwald 2013; Hein et al. 2013).

It is unclear to what extent this conclusion reflects sample bias, as there are few reports available from the southwest-ern U.S. (especially Texas and Oklahoma where there is high installed wind capacity) where a very different bat fauna is present than at most other facilities in the U.S. Higher per-centages of cave dwelling bats have been recorded at wind energy facilities in the Midwest compared to other facilities in the U.S. (Jain et al. 2011), and the few available studies

indicate that Brazilian free-tailed bats can constitute a sub-stantial proportion (41–86%) of the bats killed at facilities within this species’ range (Arnett et al. 2008; Miller 2008; Piorkowski and O’Connell 2010). However, it is uncertain whether this species is at greater risk than other bat species because the Brazilian free-tailed bat is very abundant where it occurs.

Bat fatalities peak at wind facilities in the northern U.S. during the late summer and early fall migration. 

Several studies in the northern U.S. have shown a peak in bat fatalities in late summer and early fall, coinciding with the migration season of tree bats (Kunz et al. 2007; Arnett et al. 2008; Baerwald and Barclay 2011; Jain et al. 2011; Arnett and Baerwald 2013), and a smaller peak in fatalities during spring migration has been observed for some bat species at some facilities (Arnett et al. 2008).

Some bat species may be attracted to wind turbines. 

It has been hypothesized that the relatively high number of bat fatalities may be explained by attraction to wind tur-bines or wind facilities (Horn et al. 2008; Cryan and Barclay 2009); several factors that might attract bats have been pro-posed, including sounds produced by turbines, a concentra-tion of insects near turbines, and bat mating behavior (Kunz et al. 2007; Cryan 2008; Cryan and Barclay 2009). Infrared imagery has shown bats exploring the nacelles of wind

EASTERN RED BAT, PHOTO BY MATTHEW O’DONNELL, FLICKR

BIRDS (CONTINUED)

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Wind Turbine Interactions with Wildlife and Their Habitats: A Summary of Research Results and Priority Questions

turbines from the leeward direction, especially at low wind speeds (Cryan et al. 2014). Analysis of bat carcasses beneath turbines indicate that bats are foraging for insects around wind turbines (Bennett et al. 2017; Foo et al. 2017). Large percentages of male hoary, eastern red, and silver-haired bats carcasses found during periods of high fatality levels were at sexual readiness (Cryan et al. 2012).

Barotrauma does not appear to be an important source of bat mortality at wind energy facilities. 

Forensic examination of bat carcasses found at wind energy facilities suggests that the importance of barotrauma, i.e., injury resulting from rapidly altered air pressure caused by fast-moving wind turbine blades (Baerwald et al. 2008), is substantially less than originally suggested (Rollins et al. 2012; Grodsky et al. 2011). The barotrauma hypothesis remains inadequately tested at this time.

Weather patterns may influence bat fatalities. 

Bat activity is influenced by nightly wind speed and tem-perature (Weller and Baldwin 2012), and some studies indicate that bat fatalities occur primarily on nights with low wind speed. Other weather-related variables such as temperature, wind direction, or changing barometric pres-sure may also be important (Baerwald and Barclay 2011). Additional research on weather patterns as a predictor of bat activity and fatalities could support mitigation efforts to reduce bat fatalities (Arnett et al. 2008; Baerwald and Bar-clay 2011; Weller and Baldwin 2012; Arnett and Baerwald 2013).

It is uncertain whether collision risk is higher for male migratory tree bats than female tree bats.

Examination of external characteristics of bat carcasses collected at wind energy facilities indicated that the sex ratio of migratory tree bats was skewed towards males (Arnett et al. 2008), although other studies had shown fe-male-bias or no bias (Baerwald and Barclay 2011). Bats can be a challenge to age and sex from external characteristics, especially when carcasses have decomposed or have been partially scavenged. Molecular methods used to sex bat carcasses indicate that sex ratios in fatalities of tree bats are not male-biased, although male bias in fatalities may exist in other species such as evening bats (Korstian et al. 2013).

POPULATION-LEVEL CONSEQUENCES OF COLLISION FATALITIES

Reported levels of fatalities for some bird and bat species have raised concern for potential adverse impacts to popu-lations.

The estimated total number of bird collision fatalities at wind energy facilities is likely several orders of magnitude lower than other leading anthropogenic sources of avian mortality.

Several recent estimates indicate that the number of birds killed at wind energy facilities is a very small fraction of the total annual anthropogenic bird mortality and two to four orders of magnitude lower than mortality from other an-thropogenic sources of mortality, including feral and domes-tic cats, power transmission lines, buildings and windows, and communication towers (Longcore et al. 2012; Calvert et al. 2013; Loss et al. 2014a,b,c; Loss et al. 2013a,b; Erickson et al. 2014).

HOARY BAT, PHOTO BY DANIEL NEAL, FLICKR

HORNED LARK, PHOTO BY KENNETH COLE SCHNEIDER, FLICKR

BATS (CONTINUED)

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Wind Turbine Interactions with Wildlife and Their Habitats: A Summary of Research Results and Priority Questions

Fatality rates at currently estimated values do not appear likely to lead to population declines in most bird species.

For small passerine species, current turbine-related fatalities constitute a very small percentage of their total population size (typically <0.02%), even for those species that are killed most frequently (Kingsley and Whittam 2007; Kuvlesky et al. 2007; Erickson et al. 2014). However, detailed demographic modeling indicates a potential for population-level impacts at current or projected levels of collision fatalities of some raptor species (Carrete et al. 2010; Bellebaum et al. 2013; Hunt et al. 2017).

The status of bat populations is poorly understood, and the ecological impact of bat fatality levels is not known.

Bats are long-lived, and many species have relatively low reproductive rates, making populations susceptible to local-ized extinction (Barclay and Harder 2003; Jones et al. 2003). Population sizes for migratory tree bat species are unknown, and we don’t know whether current or future collision fatality levels represent a significant threat to these spe-cies (Kunz et al. 2007; Arnett et al. 2008; Arnett and Baer-wald 2013). Studies have focused on estimating effective population sizes of tree bats from genetic data, and these

estimates might be useful as baselines for evaluating future impacts of collision mortality and other threats to bats (Korstian et al. 2015; Vonhof and Russell 2015; Sovic et al. 2016). Detailed demographic modeling indicates a potential for population-level impacts at current or projected levels of collision fatalities for hoary bats (Frick et al. 2017).

The ecological implications of White-Nose Syndrome and collision fatalities for bats are not well understood.

White-Nose Syndrome (WNS) is a fungus-caused disease that is estimated to have killed millions of bats in North America since it was first discovered (Frick et al. 2010; Turner et al. 2011; Hayes 2012). Cave-dwelling bats are most at risk, and it is unknown whether WNS will be a significant source of mortality in migratory tree bats that appear to be most vulnerable at most wind energy facilities in the U.S. Migratory tree bats rarely occur in caves, and their solitary nature may not facilitate the spread of fungal spores (Foley et al. 2011). Because cave-dwelling bats represent a higher percentage of fatalities at midwestern wind energy facilities, there is concern about the added mortality of wind turbine collisions to WNS-vulnerable bat species in this region, some of which may have declined in numbers by more than 90% (Frick et al. 2010).

DILLON WIND POWER PROJECT, PHOTO BY IBERDROLA RENEWABLES, INC., NREL 16105

POPULATION-LEVEL CONSEQUENCES OF COLLIOSION FATALITIES (CONTINUED)

Wind Turbine Interactions with Wildlife and Their Habitats: A Summary of Research Results and Priority Questions

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AVOIDANCE AND MINIMIZATION OF COLLISION FATALITIES

SitingSubstantial effort is made to estimate collision risk of birds and bats prior to the siting, construction, and operation of wind energy facilities under the premise that high-activity sites will pose an unacceptable risk to these species and should be avoided. Many wind energy companies choose to apply a tiered decision-making process as outlined in the Land-based Wind Energy Guidelines issued by the U. S. Fish and Wildlife Service in 2012. This approach, developed with input from multiple stakeholders, outlines a series of steps companies can take to identify potential risk to species thought to be at risk from wind energy development.

Siting individual turbines away from topographic features that attract concentrations of large raptors may reduce raptor collision fatalities at wind energy facilities. 

Some analyses have indicated a relationship between raptor fatalities and raptor abundance (Strickland et al. 2011; Carrete et al. 2012; Dahl et al. 2012), although studies also suggest that raptor activity as measured by standard activity surveys may not correlate with fatality rates (Ferrer et al. 2012). Large raptors are known to take advantage of wind currents created by ridge tops, upwind sides of slopes, and canyons that are favorable for local and migratory movements (Bednarz et al. 1990; Barrios and Rodriguez 2004; Hoover and Morrison 2005; de Lucas et al. 2012; Katzner et al. 2012).

The relationship between bird behavior and bird collision risk, especially near the rotor swept area, is complex and not well understood.

The foraging behavior of some spe-cies, such as red-tailed hawk, may take them into close proximity to the

rotor-swept zone and possibly explain relatively high fatality rates. Other species, such as common raven, fly around wind turbines and appear to actively avoid collisions with turbines (Kingsley and Whittam 2007; Kuvlesky et al. 2007). High prey density (e.g., small mammals) is presumed to be a principal factor responsible for high raptor use and collision rates at the Altamont Pass wind resource area (Kingsley and Whittam 2007; Kuvlesky et al. 2007; NAS 2007; Smallwood and Thelander 2008). Bayesian models of raptor collision risk have been developed to predict fatalities based on observed raptor activity in the area and estimated collision probability (New et al. 2015).

The ability to predict collision risk for birds and bats from activity recorded by radar and acoustic detectors, respectively, remains elusive.

The use of radar and bat acoustic detectors is a common feature of pre-construction risk assessments for siting wind energy facilities (Strickland et al. 2011). To date, stud-ies have not been able to develop a quantitative model enabling reasonably accurate prediction of collision risk to birds and bats from these surveys (Hein et al. 2013). Predicting bat collision risk using pre-construction activity measures would be further complicated if bats are attracted to wind turbines (see above).

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Wind Turbine Interactions with Wildlife and Their Habitats: A Summary of Research Results and Priority Questions

Variation in bat fatality rates may be influenced by landscape features affecting activity and migration routes.

Migratory-bat activity may be influenced by landscape features such as valleys, ridgelines, and riparian systems and the variation in activity among these features may be related to the geographical variation in fatality rates (Baer-wald and Barclay 2009). Relating fatality rates to landscape features around a wind energy facility could be useful in sit-ing wind farms to avoid higher-risk areas (Kunz et al. 2007; Kuvlesky et al. 2007; NAS 2007; Arnett et al. 2008).

OperationsWind energy companies are also employing a variety of technologies and operational techniques to minimize fatali-ties of vulnerable species at operating wind energy facilities.

Curtailing blade rotation at low wind speeds results in substantial reductions bat fatalities. 

An examination of ten separate studies (Baerwald et al. 2009; Arnett et al. 2011; Arnett et al. 2013b) showed reductions in bat fatalities ranging from 50 to 87% when compared to normally operating turbines. Further study to identify times when bat collision risk is high could optimize timing of curtailment and minimize power loss (Weller and Baldwin 2012; Martin et al. 2017; EPRI 2017).

Selective shutdown of high-fatality turbines may be an effective strategy for reducing fatalities of some raptor species.

Some of the highest raptor fatality rates have been ob-served in southern Spain where raptors congregate to cross the Strait of Gibraltar to Africa during migration (Ferrer et al. 2012). One study (de Lucas et al. 2012) reported a substan-tial reduction of griffon vulture fatalities (mean of 50.8%) at a facility due to selective shutdown of turbines where the greatest number of fatalities was observed.

The use of ultrasonic transmitters may deter bats away from rotor swept areas and reduce bat fatalities.

Experimental trials have shown that ultrasonic devices can reduce bat activity and foraging success, and evaluation of similar devices installed on wind turbines has shown some reduction in bat fatalities over control turbines (Arnett et al. 2013a). Development of bat deterrents using both acoustic

and visual stimuli remains an active area of research (EERE 2015).

Efforts intended to increase turbine visibility and reduce collision fatalities have met with limited success.

Impact minimization methods that are assumed to make turbine blades more visible to birds have been proposed to reduce collisions with wind turbines. For example, it has been hypothesized that towers and blades coated with ultraviolet (UV) paint may be more visible to birds, making them easier to avoid. In the only known test, Young et al. (2003) compared fatality rates at turbines with UV coatings to turbines coated with standard paint and found no differ-ence. Several raptor species have shown little response to ultraviolet light (Hunt et al. 2015). Few data are otherwise available on the effectiveness of these and other potential methods for making turbines more visible to birds.

WHOOPING CRANES, PHOTO BY GILLIANCHICAGO, FLICKR

AVOIDANCE AND MINIMIZATION OF COLLISION FATALITIES (CONTINUED)

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Wind Turbine Interactions with Wildlife and Their Habitats: A Summary of Research Results and Priority Questions

HABITAT-BASED IMPACTS ON BIRDS

Species’ use of habitat can be affected by the construction and operation of a wind energy facility. Impacts can include disturbance, displacement from suitable habitat, or demo-graphic effects due to fragmentation of habitat. The section below outlines what is known and where there is remaining uncertainty about habitat-based impacts on birds.

Operating wind energy facilities can reduce abundance of some bird species, but the effect is not consistently observed in all studies.

Studies have indicated displacement of bird species in response to wind energy development, with some species showing consistent decreases in abundance in proximity to turbines, while other species showed no effect (Hatchett et al. 2013; Loesch et al. 2013; Stevens et al. 2013; Shaffer and Buhl 2016).

It has been suggested that high site fidelity in some grass-land bird species may reduce displacement effects in the short-term and displacement would become more pro-nounced over time, but this effect was not apparent in a 10-year study of grassland birds (Shaffer and Buhl 2016). It is also unknown whether bird species will habituate to wind energy facilities and whether disturbance effects diminish over time (see Shaffer and Buhl 2016). In a UK study, three species declined in abundance during construction of wind energy facilities; the effect persisted for two of the species, both shorebirds, but red grouse density returned to pre-construction levels after the facility became operational (Pearce-Higgins et al. 2012).

There is concern that prairie chickens and greater sage-grouse will avoid wind energy facilities because of disturbance or because they perceive turbine towers as perches for avian predators.

Research indicates that close proximity to roads, utility poles or lines, trees, oil and gas platforms, and/or human habita-

tions causes displacement in prairie chickens and sage-grouse (Robel et al. 2004; Kingsley and Whittam 2007; Kuvlesky et al. 2007). It is hypothesized that similar effects would result from wind energy development, but few published studies have tested this hypothesis (Walters et al. 2014).

An extensive and comprehensive multi-year study of greater prairie chickens in a fragmented Kansas landscape showed neutral, positive, and negative responses to wind energy development as measured by a variety of demographic pa-rameters. There was little or no response in nesting females (Winder et al. 2013; Winder et al. 2014); lek persistence appeared to be lower in proximity to turbines, but there was no detectable effect of turbine proximity on male body mass (Winder et al. 2015).

A multi-year study of greater sage-grouse in Wyoming found that many demographic and habitat use factors, including selection of nest sites and nest, brood, and female survival were not influenced by proximity to turbines (LeBeau et al. 2017a). However, selection of brood rearing and post-rear-ing habitat was negatively influenced by ground disturbance related to roads and turbine pads (LeBeau et al. 2017a). Negative trends in male lek attendance were not detected (LeBeau et al. 2017b).

It is unknown whether wind energy facilities act as barriers to landscape-level movements by big game and other large terrestrial vertebrates.

There are a small number of studies that have evaluated the hypothesis that land-based wind energy facilities nega-tively affect non-volant, i.e., non-flying, wildlife. Proximity to a wind energy facility did not affect winter survival of pronghorn in Wyoming (Taylor et al. 2016). Development and operation of a wind energy facility in Oklahoma had no measurable impact on radio-collared Rocky Mountain elk (Walter et al. 2006). Long-term studies of desert tortoise at a California wind energy facility have found no negative ef-fects on tortoises using the area encompassed by the facility (Lovich et al. 2011; Ennen et al. 2012); survival of tortoises was higher within the area of the facility than in an adjacent undisturbed area (Agha etal. 2015).

About AWWIThe American Wind Wildlife Institute is a partnership of leaders in the wind industry, wildlife manage-ment agencies, and science and environmental organizations who collaborate on a shared mission: to facilitate timely and responsible development of wind energy while protecting wildlife and wildlife habitat. We envision a future where wildlife and wind energy thrive, allowing all of us — wildlife and habitat included — to reap the climate change mitigation benefits that wind energy makes possible.

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Suggested Citation: American Wind Wildlife Institute (AWWI). 2018. Wind Turbine Interactions with Wildlife and Their Habitats: A Summary of Research Results and Priority Questions. Washington, DC. Available at www.awwi.org.